How Slime Mold Can Design Efficient Subway Systems Without Human Help

Humans have always been a bit arrogant when deciding the intelligence of other creatures. We defined humanity by our ability to make tools until Jane Goodall’s observations of chimpanzee intelligence proved we didn’t have a monopoly on it. More amusingly, the attempts to build trash cans that are too difficult for the bears to use highlights the intelligence overlap between the bears and many tourists.

But a recent study published in Scientific reports suggests that there is one area where humans are at least matched by simple slime mold: getting resources from point A to point B as efficiently – and as robustly – as possible.

Mussels and men

A slime mold is one of many eukaryotic organisms known to look like blobs of slime. The most studied slime mold, Polycephalic Physarum, is a “true” slime mold type slime mold. It is a single cell with many nuclei that can reach 0.6 meters in diameter and move at a speed of 4 centimeters per hour.

As it grows, it creates a network of tubes that grow outward from its center, blindly reaching nutrients from its surroundings.

Contractions of the tubes move nutrients and encourage growth in areas close to food, while causing redundant sections of the network to die back. Given enough time, the slime will cover a given area with an effective network to get nutrients around its body.

This kind of slime is also capable of performing some pretty amazing feats. For example, it can solve mazes by growing and shrinking, modifying its structure to account for resource changes, and even exhibiting something resembling memory.

Some have proposed using slime as a “biological computer”, as it reacts predictably to external stimuli under certain conditions.

subway mud

Building on previous studies suggesting that mud can design better and more robust networks than human planners, a team of researchers, led by Raphael Kay of the University of Toronto, created a computer model of Polycephalic Physarum to see if it could help design urban transport systems.

The model allows to simulate different environments with different variables for the network, such as the total length of the segments, the time taken to move between the points and the delays caused by the deletion of a segment.

The accuracy of the model was confirmed by comparing it to real molds in a petri dish, which showed that it performed remarkably similar to its real inspiration.

They then used the model to try to recreate part of the Toronto subway.

The mold model was able to create a robust metro system that covered the city, with equivalent travel times, and was “about 40% less vulnerable to failures than the existing metro system” – meaning that if a segment of the system failed, it was more likely to continue operating efficiently, with smaller increases in travel time.

However, the “cost” factor – determined by overall length – found this system to be more expensive. The mold model struggled to design a system at the same cost; with this setting fixed, the vulnerability was the same and the travel times were actually 10% longer than the real system.

The model fared better on the funnier problem of touring Canada’s Wonderland – the largest theme park in Canada. The locations to travel between were based on actual locations: rides and food stalls. The slime model created a 10% faster and much more efficient network in the event of a segment closure.

The mold did much better than the designers of the amusement park, as the authors explain: “For an equivalent cost, we generated a network that was more than 80% less vulnerable…and almost 10% less time-consuming…than the existing system. ”

However, they noted that the park’s designers may not have built their transit system to be as efficient as possible for their own reasons.

Previous studies on this topic have shown that this type of mud can also do a great job of figuring out how to get nutrients around a simulated map of Tokyo, with the end result resembling remarkably the layout of Tokyo’s existing transit system. Tokyo.

Here is the video of how this mold did it:

Why are slime molds so good in urban planning?

Lead author Raphael Kay attributes much of the mold’s relative intelligence to having eternities of extra time to solve what is essentially a problem similar to what human planners do.

As he told Phys.org, “Humans aren’t the only ones facing the challenge of designing efficient and resilient networks. In architecture school, human architects taught us the lessons of past human architecture. But slime mold has been shaped by hundreds of millions of years of evolution, so in that sense they’re much more experienced at solving certain architectural problems than we humans ever could be.

One of the problems for human designers has been changing ideas about what the ideal city really looks like. Consider Ebenezer Howard’s utopian visions of garden cities – designed to be circular, with wide streets radiating from the center and connected to other similar cities by rail – and Le Corbusier’s Radiant City which features linear streets , skyscrapers and a form based on the human body for the sake of industrial efficiency.

These two ideas serve wildly different purposes, and cities based on these ideas look and function very differently.

Slime, however, lacks philosophy and instead maximizes efficiency without taking detours to explore trendy ideas. The fact that it doesn’t have to deal with existing zoning laws also means it’s free to behave exactly as it tends to without having to compromise, which few city planners can appreciate. .

The study authors noted that their model can “serve as an urban design tool that offers biology-based rules for building networks.” Due to the efficiency of the systems built by Physarum perhaps, we could one day compare our transport networks to those that the mud would create as a kind of efficiency benchmark.

Will you ever take a route to work that has been approved for slime mold? May be. At least your local city planners can turn to the mud for a second opinion when designing new networks. (And if anyone from the Chicago Transit Authority is reading this, slime mold is saying build the circle line!)

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